1. Field of the Invention
The present invention relates generally to a connector attached to an end portion of an optical fiber for optical connection of the optical fiber to an end of another optical fiber, and a method suitable for producing the same. More particularly, the present invention is concerned with such an optical fiber connector which is simple in construction and highly durable, and an improved method for producing the same.
2. Discussion of the Prior Art
Optical fibers have been recently used as communication cables in data communication systems. These optical fibers are formed of glass fibers or plastic materials. From the standpoint of cost of manufacture, the plastic optical fibers have been increasingly substituted for the optical fibers of glass materials. The optical fibers are connected end to end for long-distance data communication, or connected to various optical devices. For this purpose, an optical fiber connector as indicated at 1 in FIG. 17 is known.
Described more specifically, the optical fiber connector 1 includes a body 3 having a recess 2 formed in its upper surface, and a covering member 4 which engages the recess 2. The body 3 is provided with a plurality of first engagement projections 5 formed on opposite inner side surfaces of the recess 2, while the covering member 4 is provided with a plurality of second engagement projections 7 formed on its lower surface. These first and second engagement projections 5, 7 cooperate with each other to grip and hold an optical fiber 6 when the recess 2 is closed by the covering member 4.
The body 3 is formed with a connecting portion 8 extending from an outer surface thereof. The connecting portion 8 is a generally rectangular member having a square opening formed therethrough in the direction of extension. The body 3 has an extension sleeve 9 which extends through the square opening of the connecting portion 8. The extension sleeve 9 has a hole 9a whose diameter is determined so as to accommodate an end portion of a core 6a of the optical fiber 6. The core 6a has a high refractive index and is covered by a clad layer having a comparatively low refractive index.
The body 3 has two round holes 10 formed through the opposite side walls such that the two holes 10 are aligned in coaxial relation with the hole 9a of the extension sleeve 9. The hole 10 communicating with the hole 9a is not shown in FIG. 17. The holes 10 have diameters sufficient to accommodate the diameter of a sheath 6b of the optical fiber 6. To attach the optical fiber 6 to the connector 1, the sheath 6b is removed from the end portion of the fiber 6 to expose the core 6a, and the end portion of the fiber 6 is inserted through the holes 10 such that the exposed end portion of the core 6a is received within the hole 9a of the extension sleeve 9. Then, the covering member 4 is installed in the recess 5 such that the sheath 6b is gripped at its diametrically opposite position by the first and second engagement projections 5, 7, as shown in FIG. 18. By connecting the body 3 of the connector 3 at its connecting portion 8 to a desired optical device or component, the core 6a of the optical fiber 6 is optically connected to the device or component.
Another type of an optical fiber connector as indicated at 12 in FIG. 19 is also known in the art. The connector 12 is an injection-molded article which has a large-diameter hole 11a, and a small-diameter hole 11b which is aligned with the large-diameter hole 11a. To fix the optical fiber 6 to this connector 12, the circumferential surface of the sheath 6b of the optical fiber 6 is coated with a suitable adhesive, and the end portion of the fiber 6 is inserted through the connector 12, such that the exposed end portion of the core 6a is received in the small-diameter hole 11b, while the end portion of the sheath 6b received in the large-diameter hole 11a is bonded to the inner surface of the hole 11a.
However, the optical fiber connector 1 shown in FIG. 17 suffers from a tendency that the optical fiber 6 is easily separated or pulled off from the body 3 when a tensile force is applied to the connector 3 or optical fiber 6. Namely, a relatively small tensile force applied to the connector or optical fiber 3, 6 may exceed a friction force between the sheath 6b of the optical fiber 6 and the engagement projections 5, 7 of the body 3 and covering member 4 which grip the sheath 6b. Further, the connector 1 has a comparatively large number of components and tends to be large-sized.
While the above problem is not encountered on the connector 12 shown in FIG. 19, the connector 12 as well as the connector 1 suffers from another problem. That is, the hole 9a formed through the extension sleeve 9 of the connector 1 and the small-diameter hole 11b formed through the connector 12 are larger in diameter than that of the core 6a of the optical fiber 6, so that these holes 9a, 11b may receive the core 6a. Consequently, the core 6a is more or less misaligned with the hole 9a, 11b, and is therefore offset from the axis of an optical fiber to which the core 6a of the fiber 6 is optically connected. This results in a reduced area of optical communication at the connected ends of the two optical fibers, and an increased amount of optical propagation loss. In some instances, an aqueous component may enter a gap or clearance formed around the outer circumferential surfaces of the cores at the connected ends of the optical fibers. The aqueous component may have an adverse effect on the optical signal transmission through the optical fibers.